The present invention relates generally to container end panels and more particularly to panels that are utilized in conjunction with containers that are used for packaging products under high pressure, such as beer and/or carbonated beverages.
In recent years, many of these products have commonly been packaged in metal containers formed either of aluminum or tinplated steel. Since the beer and carbonated beverage industry utilizes at least 46 billion containers annually in the United States, it is essential that the containers be formed of a minimum thickness of metal so that the container can be marketed at a competitive price. The cost of the container is extremely important since, for many products, the cost of the container approaches or exceeds the cost of the product being packaged therein. As such, any cost reduction in manufacturing finished containers is extremely desirable.
Because of the large market for metal containers, particularly those formed of aluminim, a very small savings in the amount of material for a single container can substantially effect the overall cost considerations. For example, a reduction in metal thickness of approximately 0.001 inches can result in millions of dollars in savings for a manufacturer of cans.
In recent years, many beverages have been packaged in what is commonly referred to as a two-piece container. In this container, the bottom wall and sidewall are formed as an integral unit by drawing and ironing a flat blank to produce a container body open at one end. The open end of the body then has an end panel secured thereto by a conventional seaming process.
When these types of containers are utilized for packaging beer and/or carbonated beverages, the containers must be capable of withstanding minimum pressures of 90 psi before the container end will "buckle" and also be capable of withstanding minimum pressures of 60 psi before the container will "rock". The term "rock" is related to the deflection of the center panel portion of the end panel, which normally has a tab connected thereto by a rivet, and the term identifies the pressure at which any given portion of the center of the end panel projects above the upper peripheral edge or chime of the container. The term "buckle" pressure is the pressure that an end is capable of withstanding without any notable distortion of the end and/or rupture of any portion of the end.
Quite recently the assignee of the present invention developed a drawn and ironed container that can be manufactured with a minimum amount of metal and still be capable of withstanding the pressures indicated above. This drawn and ironed container is disclosed in U.S. Pat. No. 3,942,673 issued to Seung W. Lyu et al. While this drawn and ironed container has found a remarkable degree of commercial success, the end panel utilized in connection therewith still of necessity must be formed from a metal blank having a thickness of approximately 0.013 inches to withstand the desired buckle and rock pressures.
Various proposals have been suggested for reducing the metal thickness of an end panel. One example of such proposal is disclosed in Cospen et al. U.S. Pat. No. 3,843,014. This patent discloses a particular configuration for the countersink portion of an end panel between a peripheral curl and a center flat panel portion. The patentees of this patent indicate that the particular configuration of the end panel will allow a panel to be formed from metal having a thickness on the order of 0.0115 inches. Actual tests were conducted with sample end panels constructed in accordance with the teachings of the Cospen et al. disclosure and it was found that while the container end panel was capable of withstanding the minimum buckle pressures required, the particular configuration resulted in the end being bulged outwardly sufficiently at approximately 30 psi to produce a "rocker" container. Thus, such a proposal has not been accepted as a commercially feasible alternate to the present commercial ends.
Another more recent proposal for utilizing sheet metal stock of less thickness than the standard indicated above has been developed by Aluminum Company of America, Pittsburgh, Pa., which is disclosed in U.S. Pat. No. 4,031,837. This proposal contemplates increasing the depth of the center panel with respect to the lower edge of the outer countersink above the present standard of 0.065 inches for a conventional 209 diameter aluminum beer and beverage end. While test data from the developer of this product indicates that the container is capable of withstanding the minimum required buckle pressures, the particular configuration of the end requires new seamer chucks for double seaming the end panel onto a container body. Such an approach is unrealistic from a commercial standpoint since most packagers will utilize various types of ends from different manufacturers and these ends of necessity must be capable of being double seamed to a container utilizing a standard chuck seamer. For example, a packager may make one run utilizing a certain end manufactured by one company and then shift to a further end manufactured by another company. If different types of chuck seamers are required for the various operations, a substantial amount of time and cost will be involved in converting the seamers to accommodate different ends. This approach also requires that the diameter of the blank used for making the end be increased.